The present invention relates to a method for epitaxially forming a monocrystalline layer of a material such as silicon or germanium. More particularly, it relates to a process for fabricating a monocrystalline layer through an aperture in a mask which is disposed on an appropriate crystalline substrate.
Structures incorporating a monocrystalline silicon layer overlying a mask layer can potentially have a significant impact in the semiconductor industry. For example, the ability to fabricate monocrystalline silicon over an insulating silicon dioxide mask layer makes possible the fabrication of a "three dimensional" integrated circuit wherein devices in a given monocrystalline layer might overlie, yet be isolated from, devices in an underlying monocrystalline silicon layer.
A method for fabricating a monocrystalline silicon layer over a non-crystalline layer such as silicon dioxide is disclosed in copending and commonly assigned U.S. patent application Ser. No. 338,958, Method for Growing Monocrystalline Silicon on a Mask Layer, J. F. Corboy, Jr. et al., filed Jan. 12, 1982. In the fabrication technique disclosed therein, a semiconductor substrate is provided, the substrate having a monocrystalline portion at a surface thereof. A mask layer of a material such as silicon dioxide is formed over the substrate surface, and an aperture corresponding to a monocrystalline portion of the substrate is generated in the mask layer. Silicon is then epitaxially deposited from a gas mixture which comprises a silicon-source gas, and a carrier gas. The substrate is next exposed to a gas mixture comprising an etching gas and a carrier gas such that a portion of the previously deposited silicon is etched. The deposition and etching cycle is then repeated an appropriate number of times so as to achieve a monocrystalline silicon layer of predetermined size on the mask layer.
As disclosed herein, we have now discovered that the quality of a deposited monocrystalline film is strongly dependent upon the configuration and orientation of the mask aperture.